A meaning

A as a noun

1. a metric unit of length equal to one ten billionth of a meter (or 0.0001 micron); used to specify wavelengths of electromagnetic radiation

   Synonyms: angstrom, angstrom unit

   Type of: metric linear unit

2. any of several fat-soluble vitamins essential for normal vision; prevents night blindness or inflammation or dryness of the eyes

   Synonyms: vitamin A, antiophthalmic factor, axerophthol

   Type of: fat-soluble vitamin

   Kinds: vitamin A1, vitamin A2

3. one of the four nucleotides used in building DNA; all four nucleotides have a common phosphate group and a sugar (ribose)

   Synonyms: deoxyadenosine monophosphate

   Type of: nucleotide

4. (biochemistry) purine base found in DNA and RNA; pairs with thymine in DNA and with uracil in RNA

   Synonyms: adenine

   Type of: purine

5. the basic unit of electric current adopted under the Systeme International d'Unites
   • a typical household circuit carries 15 to 50 amps

   Synonyms: ampere, amp

   Type of: current unit

6. the 1st letter of the Roman alphabet

   Type of: letter

7. the blood group whose red cells carry the A antigen

   Synonyms: type A, group A

   Type of: blood group

How to pronounce A

A is pronounced /ə/ in British English and /ə/ in American English. It has 1 syllable.